1. Field of the Invention
The present invention relates to a copying machine in which the magnifying power for copying may be varied, and more particularly to improvements of the control section thereof for driving an original-scanning optics unit.
2. Description of the Prior Art
A variable magnification type copying machine will first be explained with reference to FIGS. 1 to 3.
In FIG. 1, an optics unit 3 is disposed above a photosensitive drum 2 and is driven in the direction of the reference arrow to scan originals placed on a document glass plate 2. An original image is thereby focussed on the surface of photosensitive drum 1 by optics unit 3, and the electrostatic latent image is then developed with toners while passing through a development device 4. The toner image on the surface of photosensitive drum 1 is next transferred onto transfer paper X fed from paper feeding device 5, and is then conveyed to fixing device 7 by conveyance device 6. Paper feeding device 5 includes paper feeding rollers 9a and 9b which draw individual sheets of transfer paper X from cassette 8a or 8b, respectively and, having been drawn into the passageway for feeding papers, the transfer sheets are received through paper registration roller 10. Momentary-stop detector 11 is provided in the paper feeding passage to detect the front and rear ends of transfer paper X. A paper ejecting detector 13 is similarly provided in paper ejecting roller device 12 to detect the rear or trailing end of transfer paper X.
The optics unit 3 for slit exposure of an original to light is equipped with a primary movable table 16 carrying an exposure lamp 14 and primary mirror 15. The light reflected from primary mirror 15 is made incident upon a lens 20 through secondary mirror 18 and tertiary mirror 19 of a secondary movable table 17, table 17 being synchronously moved with primary movable table 16 at one-half the moving speed of table 16. Lens 20 focuses the original image onto the surface of photosensitive drum 1 through a quaternary mirror 21. In addition, an initial position detector 22--for detecting the initial position of optics unit 3--and paper feeding start detector 23--to start the rotation of paper registration roller 10--are provided in the movement locus of a cam 16A of primary movable table 16.
FIG. 2 illustrates the structure of the control section for driving optics unit 3, wherein a driving drum 24, by which primary movable table 16 and secondary movable table 17 are reciprocated, is driven by a connecting member such as chain 26 which is, in turn, driven by a driving device such as motor 25. Thus, optics unit 3 is driven by a driven device through the medium of a connecting member. A forward clutch 27 and a return clutch 28 are interposingly provided, between driving drum 24 and chain 26, to switch the direction of rotation of driving drum 24. Forward clutch 27 is arranged for engagement by the copy start signals and is disengaged by the rear or trailing edge detecting signals from momentary-stop detector 11; return clutch 28 is arranged for engagement by the rear edge detecting signals from momentary-stop detector 11 and is disengaged by the initial position return signals from initial position detector 22.
FIG. 3 illustrates a position adjustment mechanism for lens 20, wherein a lens board 29 carrying lens 20 is movable along the double-headed reference arrow by an auxiliary motor 30 actuated by command from an actuation mode selecting button selected by an operator. A plurality of lens position detectors 31, 32 and 33 are disposed to sense the position of lens board 29 and to detect whether the position of board 29 corresponds to a designated actuation mode.
In the variable magnification type copying machine thus far disclosed, the distance of forward movement of optics unit 3 is to be determined by the time period extending from when paper registration roller 10 starts to rotate and concluding when momentary-stop detector 11 detects the rear edge of transfer paper X. This advantageously assures that any necessary distance of forward movement--irrespective of copy magnifying power--and the time required for continuous copying, are shortened. In addition, the control circuit and program can be simplified more than those used in other kinds of machines, wherein the distance of forward movement of the optics unit is designed in accordance with the selected actuation mode thereof. Where a magnification type copying machine is designated for reduction copying, there is no problem, though, if transfer paper of a size appropriate for receiving the reduced original image is used; there are, however, instances where it is required to obtain copies reduced in size on a portion of a sheet of transfer paper having an unnecessarily larger size. Where, for example, a copying machine is designed to use both transfer paper and originals of A-3 size and also to provide a reduction ratio of 0.71, the length of the document glass plate 2 is 420 mm (which is the same as the length of A-3 size that will do), but the distance of forward movement of the optics unit 3 extends for approximately 591 mm and the copying machine therefore becomes very large in size.
There are also instances in which an operator may utilize transfer paper of which only the length is extraordinarily long and, when such extraordinary size papers are used, problems can develop in that the driving section of the optics unit may cause some damage in the general machine construction heretofore illustrated and described.